1. Field of the Invention
The present invention relates to a logical unit number increasing device and a logical unit number increasing method for increasing the number of logical units of a magnetic disk device, an optical recording and reproducing apparatus, a magneto-optical recording and reproducing apparatus, a semiconductor recording and reproducing apparatus, or the like connected to a computer.
2. Description of the Related Art
In the SCSI (Small Computer System Interface) standard for connecting peripheral devices to a computer and so forth, it is possible to allocate a plurality of LUNs (Logical Unit Numbers) to one SCSI ID. On the other hand, there is a limit to the number of SCSI IDs that can be used in one SCSI bus, and there is also a limit to the number of logical unit numbers that can be allocated to one SCSI ID. For example, in the SCSI2 standard, the number of SCSI IDs is 8 at maximum, but is substantially 7 at maximum because one of them is used for a host bus adapter. The number of logical unit numbers that can be allocated to one SCSI ID is 128 at maximum in typical Linux. In this case, assuming that a computer has one SCSI bus and one logical unit is allocated to each logical unit number with respect to each SCSI ID, it is possible to use 7×128=896 logical units at maximum. However, there are those instances where more than 896 logical units are required.
On the other hand, in WINDOWS (registered trademark) one drive letter composed of one alphabet is allocated to each logical unit so that only 26 logical units can be connected to a computer at maximum. Further, in WINDOWS (registered trademark), one drive letter is allocated to each logical unit having one logical unit number with respect to each SCSI ID. For example, if there are 5 logical unit numbers with respect to a certain SCSI ID, only 5 drive letters can be allocated to that SCSI ID.
In order to solve this problem, a plurality of CD-ROM devices are allocated to one drive letter as described in, for example, JP-A-H09-265360.
However, the described technique aims to improve a CD service program, and therefore, although the CD-ROM devices can be connected in a number exceeding a limit, this is not the case with respect to magnetic disk devices that have been widely used as external storage devices.
Further, when many storage devices are simultaneously recognized, there is a possibility of destroying data of an unexpected device by a wrong operation or the like.